The present invention relates to a laser processing apparatus and method, more specifically to a laser repair apparatus and method for processing wiring patterns on a semiconductor wafer.
The technique of the repair processing with laser beams is for applying the laser beams with high accuracy to perform required processing for melting fuses to substantially remove defective parts cutting off wiring patterns, etc. on a semiconductor wafer. A typical repair technique is for memory ICs. Redundant cells are provided in a memory IC, and laser beams are applied to melt off fuses to change the address lines of defective cells to that of spare cells for defect remedy, which contributes to higher yields. Other repair processing techniques are trimming processing techniques for correcting resistance values and characteristics of circuit elements, etc.
After the above-described repair processing, results of the repair processing are confirmed visually by the use of, e.g., optical cameras, but it is often difficult to judge based on visual observation, whether or not the repair results are satisfactory. In a case that the repair processing is not proper, and results of the repair processing are not perfect, operations of circuits are often unstable due to transient changes, which is unpreferable in reliability.
Accordingly, it is preferable to apply energy of laser beams of a required beam spot shape to a part to be repaired with accuracy as high as possible to perform repair processing.
Relationships between beam spot diameters and focal depths in the laser beam axial direction are shown in FIGS. briefly described in the following.
As a laser beam has a smallest beam spot diameter at a focus point (hereafter used same meaning as xe2x80x9cfocal pointxe2x80x9d), and the beam spot diameter is gradually increased away from the focus point. An irradiation density is expressed by X/pr2 wherein X is a laser bean intensity, and r is a laser beam radius. Thus an irradiation density is proportional to an area of an irradiated part. In order to perform reliable, suitable repair processing, energy of a required irradiation density is applied to a required processed surface to be repair-processed.
When an amount per unit area of energy applied to a target part is small, melting off of a pattern is unsatisfactory. Reversely when an amount per unit area of energy applied to a target part is large, there is a risk that a peripheral part thereof may be damaged. Also known in the art that an allowable focal depth range depends upon an irradiation area at a focus.
A practical focal depth range varies with laser repair apparatuses, and also with processing conditions of wafers and patterns themselves formed on wafers.
In semiconductor wafers on which circuits and patterns are formed on by the recent micronization techniques the patterns have about 0.5-1,0 xcexcm width. It is necessary that laser beams are applied, focused to have spot sizes corresponding to the micronized patterns.
The beam shape with a small-diameter spot must have a focal depth suitable for repair processing. That is, a required irradiation density range with respect to an irradiation density at a focus point must be a focal depth range which is far narrower than the focal depth range.
On the other hand, wafers to be repair-processed have been subjected to various LSI fabrication processes, and have a little warp.
The warps of the processed surfaces of the wafers increase a focal depth range required for forming circuit patterns, and recent micronization of circuit patterns further increases it. The results are that the focal depth range required for forming circuit patterns sometimes exceeds an allowable focal depth range When it exceeds an allowable focal depth range, there are risks that repair processing is unsatisfactory such that adjacent peripheral micronized circuits and patterns may be damaged. Repair processing which causes such risks are quite unpreferable for repair processing requiring especially reliability.
An object of the present invention is to provide a laser repair apparatus and method which can repair-process with high accuracy wafers-to-be-repaired including those having warp.
The above-described object is achieved by a laser repair apparatus comprising a stage for a wafer to be mounted on, a laser beam source for emitting a laser beam, focus adjusting means for adjusting a focus of the laser beam, and focus point measuring means for measuring a focus point of the laser beam with respect to the wafer on the stage, a focus being adjusted by the focus adjusting means with respect to each required part-to-be-repair processed of the wafer to perform repair-processing by the laser beam on the wafer, a position at which the laser beam is focused by the focus adjusting means at a prescribed position in the required part to be repair-processed being set as a reference focus, in performing the repair processing at another position in the required part to be repair-processed, a focus point being detected by the focus point detecting means, and when the focus point is outside an allowable range from the reference position, the repair processing on the required part to be repair processed being interrupted.
A semiconductor wafer repair apparatus which can reject semiconductor wafers from a repair-processing step when a Z axial height in focus measurement exceeds an allowable value or a prescribed allowable value for a focal depth can be realized.
The above-described object is achieved by a laser repair method for measuring a focus point of a laser beam on a wafer on a stage, adjusting a focus on each required part to be repair-processed, performing repair-processing on the wafer by the laser beam, a position on which the laser beam is focused at a prescribed position in the required part to be repair-processed being set as a reference focus, when the repair-processing is performed at another position in the required part to be repair-processed, a focal point being detected at said another position, and the repair-processing being interrupted when the focus point is outside an allowable range from the reference position.
A semiconductor wafer repair method which can reject semiconductor wafers from a repair-processing step when a Z axial height in focus measurement exceeds an allowable value or a prescribed allowable value for a focal depth can be realized.
The above-described object is achieved by a laser repair method for measuring a focus point of a laser beam on a wafer on a stage, adjusting a focus on each required part to be repair-processed, performing repair-processing on the wafer by the laser beam, a position on which the laser beam is focused at a prescribed position in the required part to be repair-processed being set as a reference focus, when the repair-processing is performed at another position in the required part to be repair-processed, a focal point being detected at said another position, and the repair-processing being interrupted when the focus point is outside an allowable range from the reference position.
Repair-processing time can be saved by time to be spent on a unit of a wafer-to-be-repair processed.